Resistance unit and mounting therefor



Nbv. 24, 1936. N ONR,;D 2,062,163

RESISTANCE UNIT AND MOUNTING THEREFOR Original Filed Dec. 3l, 1927 3 Sheets-Sheet 1 Nov. 24, 1936.. N. J. CONRAD RESISTANCE UNIT AND MOUNTING THEREFOR Original Filed Dec. 51 1927 3 Sheets-Sheet 2 zcbolas J $007 00 3 Sheets-Sheet 3 Original Filed Dec. 51, 1927 Patented Nov. 24, 1 936,

UNITED STATES PATENT OFFICE RESISTANCE UNIT AND MOUNTING THEREFOR Application December 31, 1927, Serial No. 244,015

. Renewed July 18, 1935 19 Claims. (Cl. 201-67) My invention relates to an improved protective resistance and mounting therefor.

In modern alternating current generating and distributing stations, the potential transformers 5 are employed to reduce the voltage of the buses or lines to a value suitable for operating synchronizing, indicating and recording instruments. Such a potential transformer comprises a primary or high tension winding of a relatively great number of turns, an iron core and a secondary or low tension winding of a proportionally smaller number of turns. a

On the high tension or primary side, the flow ofc'urrent is normally limited by the resistance .5 and impedance of the winding, but obviously in the event of failure of insulation or a short circuit of the primary winding, there might develop an inter-phase short circuit of serious character.

' Protective fuses are generally employed, but it :0 is coming to be recognized as better practice on voltages of around 6,600 volts or greater to employ both fuses and current limiting resistances. Fuses naturally are desirable to interrupt the flow of I current, but the fuse which is normally of about 35 one half ampere rating must on high tension sus tain a very heavy overload in the event of a short circuited winding in the transformer. Hence, the

practice has arisen of inserting a high resistance in one or more of the leads of the potential trans- ;a former to limit the possible current flow in the event of a. short" circuited winding or the like.

The employment of such current limiting resistors does not appreciably interfere with the accuracy of the instrument circuit. The resist- 15 ance being inserted directly in series in the high tension connection requires suitable mounting and insulation for the voltage employed.

My invention relates to-the provision of a suitable embodiment of such a resistance and the to mounting therefor. Since on high voltages the expense of insulators runs into a considerable figure, I provide in the preferred form of my invention a combined fuse and resistor mounting} or. switch and resistor mounting upon an insul lator.

The resistance is preferably a metallic conductor of suitable character such-as nichrome or chromel wire and of such cross section and length as is required to provide the desired resistance 50 and yet be sufiicientlystrong mechanically and electrically to insure permanency under the conditions to which it is subjected in use. Preferably I form the resistance wire into an open helix of relatively small diameter like a coil spring and 55 then wind this coiled conductor upon a porcelain the primary several functionsnamely, that of forming suit-' 5 able electrical terminals and suitable mechanical mounting for connected parts and also co-operating with a glass or like sleeve to form a weather tight enclosure for the resistance element. This is particularly useful for outdoor mounting. 1o

By forming the unit as a relatively short cylinder, and of a diameter approximately the same as that of the mounting insulator it may be made structurally an extension of the upper endof the mounting insulator and fuse or switch terminals may be mounted upon the same without any lateral projection or any extension of the spacing of the insulators. Thus it becomes possible to insert the resistor unit in a mounting already installed without any disturbance of the same. The resistance unit may, of course, be mounted in a variety of ways some of whichare illustrated in the accompanying drawings.

Now in order to acquaint those skilled in the art with the manner of constructing and operating a device embodying my invention, I shall describe in connection with the accompanying drawings, a specific embodiment of the same.

Figure 1: is a side elevational view of a fuse and mounting in which the resistor of my invention is employed;

Figure 2 is a top plan view of the resistor with the top plate removed:

Figure 3 is a vertical cross section viewed as though taken on the line 33 of Figure 2;

Figure 4 is a bottom plan'view of the unit;

Figure 5 is a side elevational view of the sametaken at\ right angles to the view shown in Figure 1; r

, Figure 6 is a vertical section through'the top' 40 of the insulator sh owingthe mounting for the unit; and

Figure 7 is a side elevational view of amodifled form of,mounting.

Referring to Figure l, I have shown a mounting for a fuse I such as is employed in series with riding of a potential transformer, this fuse being of the liquid quenched type now furnished to the market by my assignee. It preferably is of the type disclosed in my copending application Serial No. 164,155, filed January-26, 1927, which issued as Patent 1,779,929, Oct. 28, 1930. The fuse comprises a central glass sleeve 2 with metallic terminal members 3 and 4 which terminal members are secured-in fuse clips 5 and 6, these fuse clips being provided with wire bails I and 8 and being preferably of the construction described and claimed in my copending application Serial No. 32,741, filedMay 25,1925, which issuedas Patent 1,665,446, April 10, 1928. The fuse mounting clips 5 and 6 are adapted normally to be secured to a suitable mounting by two machine screws passing through the bottom of the U-shaped clips as will be explained later. grounded metallic mounting frame base 9, in this case comprising a thin plate of iron suitable for attachment to a frame or other mounting supports two post type insulators l0 and l I.

These insulators have metallic inserts or end pieces l2-I2 cemented in the ends of the same and cap screws l3--l3 are passed through holes in the base 9 inserted into openings in said metallic end pieces or inserts l2 to mount the post insulators 'l0 and II upon the base 9. By the term cement I intend to include any suitable bonding material. The post insulators l0 and II are identical at opposite ends. The metallic end pieces i2-I2 are recessed and a lock washer is interposed between. the recess and the plate 9 in order to hold the insulators I0 and H against turning. At the upper ends of the insulators i0 and H suitable terminals and I5 are provided, these terminals comprising strips of copper-such as are employed for bus bars and the manner of securing the same to the upper end pieces i2 is shown more in detaii in Figure 6.

The terminal piece M has a central threaded stud l6 secured thereto as by brazing or soldering, this stud projecting down into the threaded socket ,il in the metallic end piece or insert I2. A sheet metal disc l8 provides an-crnamental cover or finish for the top of the insert or end piece l2. The recess l9 which is formed in the metallic insert I2 receives a lock washer 20 beto permit mounting directly upon said terminal piece. However in the present instance, I interpose as shown more particularly in Figures 1, 3, and 5, a cross piece 22 which is preferably made of a piece of copper barof the same cross section as the terminal members l4--'-| 5. This cross piece 22 is held upon the terminal piece l4 by the screws 2323 which extend down through holes in said cross piece22 and-thread into the threaded hole 2l2l in the terminal piece l4. The outer ends" of the cross piece 22 have threaded holes for receiving the screws 24-24 which screws 24-24 pass through lugs 2525 extending out from the side of the metallic end member 26 which end member forms the lower part of the resistance unit 21 .or 28, as the case may be.

The resistance unit 21 comprises a central short cylinder 30 of insulating material, in this case porcelain which is the preferred material for this purpose. It has depressions or cementing sockets 3l-32 formed in opposite ends to receive the cementing pins or studs 33-34 of the metallic end pieces 26 and 35, respectively. The cylinder 30 is of a diameter approximately the same as that of the mounting insulator. By attaching the end pieces 26 and 35'by axially extending anchorages, the fulllength of the cylindrical surface of the insulating core or block 30 may be occupied by the resistor 36,.

The outside cylindrical surface of the insulating member 30 is provided with a helical groove which extends the full length of the insulatorto receive the coiled resistance wire 36, which has 'one' terminal thereof secured as by the screw 31 to the lower end piece 26 and the opposite terminal thereof secured as by the screw 38 to the upper metallic end piece 35. The resistance 36 comprises a suitable resistance wire such as nichrome or chrome] wound into an open helical coil of small diameter, the convolutions of the coils being spaced far enough apart so as to avoid contacting at any time, particularly when they are wound in'place in the helical grooves on the surface of the block 30. a t

The lower end piece 26 comprises an outwardly extending flange 40 with a turned-up rim 4! at the periphery thereof.

Between the flange 40 and the cementing stud 33, there is an enlarged cylindrical portion to which the terminal ofthe coil 36 may be attached as indicated at the screw 31.

The bottom part of the lower end piece 26 is recessed as indicated at 42 to house the heads of the screws 23. The bottom of the end piece 26 and the lugs 25, 25 thereof are surface ground to provide a flat seating face for seating upon the cross piece 22.

The upper metallic member 35 which is cemented to the insulator 30 comprises the cementing stud 34 and the upper cylindrical portion 43 which has a laterally extending lug 44 forming a terminal for the upper end of the resistance coil 36. This upper cylindrical portion has a flat vide two threaded holes 454 5 for receiving the clamping screws 4646 which are of the same pitch and diameter as the screws 23-23 and are drilled on the same spacing. A sheet metal can 41 is held in place on the end piece 35 by means of two countersunk head screws 48 threaded in holes 49-49 and adapted to lie under the fuse clip 5 when the device is assembled. The sheet metal cap 41 has a down turned flange 50 and .top plate and it is drilled and threaded to probetween the flange -50 and the corresponding flange 4| on the lower end, ,a sleeve 5| of transparent material such as glass, mica, or the like, is disposed. Gaskets are preferably provided at the ends of the glass sleeve 5| to maintain a tight closure so that moisture, dust and-the like will be excluded from the interior of the casing which is formed thereby. The enclosure of the resistance conductor 36, according to my invention is of considerable commercial'importance.

, First, foreign matter, particularly conducting, dust, smoke, etc. tends to form a conducting coating, particularly in places where air movement is low, as within the helicalgroove. Such a deposit tends to short the turns of the coil within the groove and also tends to cut down the electrical creepage distance between the ends of the porcelain body, thereby changing the voltage gradient or electrostatic stress upon the porcelain body. Water isalso'excluded.

Second, the sleeve 5| performs an important service in case the resistance conductor 361s brokemor burned through. The conductor 36 is a nickeh'iron, chromium compound chromel or nichrome) and is stiff and springy. It does not lose the springiness upon being heated, and hence evenif burned through at 'someipoint, it has sufficient of its initial springiness to unwind from the porcelain body. In unwinding, it whips out and may contact with ground or alive conductor. Since it cannot be foretold when it will break or burn out, it may be that the whole length ID: the conductor is thrown out. Even if in unwinding it does not chance to strike a live or grounded part, it may hang down by gravity and decrease the distance to ground or a live part to-a dangerous point. Thus an element of danger ta the system and to the personnel is created.

e glass sleeve 5| prevents the conductor from thus uncoiling. In addition, it permits visual inspection which has been found to be highly desirable. Unless the sleeve 5| is made of a vitreous insulator, the are which may form between the adjacent ends of the severed conductor 36 may carbonizewhe sleeve. Such carbonization, not

being visible, may go unnoticed, and yet permit creepage of potential'between the severed ends, or may change the voltage gradient entirely.

The glass enclosure fulfills the requirement of This is particularly valuable where an appreciable amount of current passes though the resistor, and the energy thereof must be dissipated.

The resistor 36 is constantly in circuit and the heat developed by the fiow of current therethrough affects the temperature of the porcelain body 30. It and the connected metallic parts tend to expand and contract with heating and cooling. However, provision is made for preventing cracking of the glass sleeve 5I by such action in that first expansion of flanges 4I and 50, by heating above the temperature at which the parts are assembled, does not tend to bind or crack the glass. taking up the endwise contraction and expansion of the unit without danger of cracking the glass in part by the gaskets and in part by the provision of the sheet metal cap or head '41, which, being fastened at the center, permits of expansion and contraction of the porcelain body 30 and the metallic end pieces without imposing, any appreciable stresses upon the glass sleeve, yet maintaining a tight closure for the ends thereof.

. The resulting unit is of a diameter substantially the same as the insulator III and its axis is in substantial alignment with the insulator III so that the spacing of the fuse clips 55 remains the same when the units 21 and 28 are interposed between said fuse clips and the terminals I4--I'5.

On this account, it is possible in installations already provided to add the resistance unit in series with the fuse for the purpose of providing inherent current limiting resistance. The resistor proper being metallic and of a character which resists corrosion or fusion remains substantially constant under all conditions. It has a negligible temperature coefiicient of resistance and a high melting point. I

Dividing the total resistance into two parts, each separately mounted and enclosed, provides ent rises and a flashover between adjacent turns may result. If this once starts, the fiashover will quickly involve the entire unit. When the re- Likewise, provision is made for real importance is gained. Where no enclosing casing is provided, the division of the total resistance into two segregate units is beneficial in that if the resistance conductor be all disposed in one unit, and it burns off, the unwinding of one long resistor is far more likely to cause dis-' as'trous results than if two short-resistors be thus unwound.

' Division of the resistance in two substantially equal units disposed on the tops of the insulators has the mechanical advantage, particularlyin old installations, that the clearance at neither end of the fuse or switch is unduly decreased.

In Figure '7 I have shown a modified form of installation wherein the resistors 21 and 28 are mounted on the insulators II) and I I with the fuse mounted upon terminal members 52 and .53 extending from the junction of the resistors 21-28 and supporting insulators I0-I I. The upper terminals of the resistors 21-28 are connected to line terminals 54 and 55. The terminal members 52 and 53 comprise copper bars having switch contacts 55 and 51 secured thereto, the contact 56 being a free terminal and the contact 51 being a. hinge terminal for the switch blade 58 which switch blade, however, comprises an intermediate portion 59 of insulating material having the end contact portions- 60 and GI secured thereto and the fuse clips 5 and 6 connected upon the terminal portions 60 and 6| so as to provide a disconnecting type of fuse mounting The grounded metallic base member 9 is long enough to receive insulators Ill and I I with the increased spacing which is required by this form of mounting. In the present instance the resistors are embodied in a fuse installation in such a manner as not to increase materially the verticalheight of the installation, but an increased spacing between the insulators III and I I is necessary in Figure '7 as compared with Figure 1. Where fuses of this character are mounted in cells, there is more room in the direction of the axis of the insulators than there is along the sides or end where the resistor is to be installed in old installations.

A great variety of mountings is possible and where there is no objection to increasing the width, the disconnecting switch or the fuse alone may be mounted at the side of the resistors and insulators.

I do not intend to be limited to the details shown and described since it will be apparent to those skilled in the art that there may be numerous modifications within the scope of the appended claims.

I claim:

1. In combination, a base member, a pair of insulators mounted on the base, terminal members mounted on the tops of the insulators, relatively short cylindrical resistor units mounted on said terminals, contact members mounted upon the outer ends of the resistor units, and means electrically connecting the contact members, said resistor units providing a wire resistance connected between the contact device and the said terminal.

2. In combination, a grounded support, two

high voltage insulators mounted thereon, a resistance unit'mounted on each insulator in axial alignment therewith and insulated from ground thereby, a line clip atone end of said resistor, and means at the other end of each resistor for connecting the two resistors in anelectric circuit with the line clips.

3. In combination, a grounded support, two high voltage insulatorsmounted thereon, a resistance unit mounted on each insulator in axial alignment therewith and insulated from ground thereby, a line clip at one end of each resistance eral confines of the cylindrical surface of said body, said metallic inserts being electrically separated by insulation which structurally forms a part of said body of insulation, current limiting means comprising a coiled wire resistor wound' on said body under initial tension, said wire tending to unwind, and a sleeve of vitreous insulation enclosing said body of insulation and preventing free unwinding of the resistance wire in case of breakage of the wire, said sleeve being confined axially and radially by a removable flanged head clamped to the end surface of one of said metallic inserts.

5. In combination, a pair of insulators mounted with their axes substantially parallel, metallic end pieces upon the upper ends of said insulators, a substantially cylindrical resistance unit mounted upon the metallic end piece of each insulator with the axes of the resistance units extending in the direction of theaxes of the insulators, each resistance unit comprising a substantially cylindrical porcelain body having a helical groove on its cylindrical surface, recesses in each end, end pieces having studs anchored in said recesses, a coiled resistance conductor lying in said groove and connecting said end pieces, flanged heads on said end pieces, aglass sleeve surrounding said body and held in place by said flanged heads to enclose the resistance conductor, a conducting link including a fuse connecting the outer end pieces of said resistance units, and line terminals concircuit, and a pair of substantially cylindrical resistor units each having an insulator body and metallic end pieces-provided with coupling means adapted to matewith the coupling means of the insulator end piece and the coupling means of the fuse clip respectively, said units being mounted in axial alinement with the insulators and in turn supporting the fuse clips in alinement with the insulators, and a protective "wire resistance substantially half of which is disposed on the insulator body of each unit and connected between the end pieces of the body.

7. In a device of the class described, a base, a

.pair of hightension insulators standing on said base, said insulators having metallic end pieces provided with coupling means, a fuse having ferrules, a pair of fuse clips having bases provided with coupling means mating with said first named coupling means, and having jaws cooperating with said fuse ferrules to connect the fuse into circuit, and a pair of substantially cylindrical resistor units each having an insulator body and metallic end pieces provided with coupling means adapted to mate with the coupling means of the insulator end piece and the coupling means of the fuse clip respectively, said units being mounted in axial alinement with the insulators and in turn supporting the fuse clips in alinement with the insulators, and a protective wire resistance substantially half of which is disposed on the insulator body of each unit and connected between the end pieces of the body, the end pieces of each unit having annular flanges extending radially beyond the corresponding insulator and having axially extending rims facing each other, and .a glass sleeve for each unit centered by said rims and confined endwise by the corresponding end pieces to form a substantially dust proof housing about the insulator and its wire resistance.

8. In a high tension fuse installation comprising a pair of supporting insulators, line terminals, clips for receiving the fuse, cylindrical members of insulation constituting rigid mechanical support between the supporting insulators and the fuse clipsand electrically insulating the fuse clipsfrom the line terminals,and a pair of resist ance wires, each of substantially half the required length, one of saidresistance wires being wound around each of said cylindrical members and connecting electrically the fuse clips and the line terminals. V

9. A high tension resistance unit. comprising a substantially cylindrical insulator body of a length not substantially greater than its diameter and having a circumference and length to provide an external surface of sufiicent extent to accommodate a resistance wire of a length at least half of the length required for the purpose described, terminals at opposite ends of said insulator body, a protective wire resist me of 'a length at least half the required leng h wound around the insulator body and connected to the terminals at the opposite ends thereof, one of said terminals having .an outwardly extending flange, a glass sleeve surrounding the insulator body and closed at one end by said flange, and a flanged cap for engaging and closing the opposite end of said sleeve, said flanged cap being connected to said second terminal and separable from said second terminal to permit attachment of said second terminal to the end of the insulator body independently of the flange afforded by said cap, said flanged terminal member, said flanged cap and said glass'sleeve forming a substantially tight enclosure for the resistance unit.

10. A high tension resistance comprising in combination a cylindrical body of insulation having a resistor wound upon its external cylindrical surface, a first metallic member anchored upon one end of said body of insulation and having an outwardly extending flange forming a head, a glass sleeve resting upon said flange and having one end closed thereby, a second metallic member having anchoring means extending axially into the body of the insulator for holding said second member upon the end of-the body independently of the first member, said members being electrically separated by insulation which structurally forms part of said body of insulation, laterally facing .terminals for holding the ends of said resistor mounted on said metallic cylindrical sleeve. of glass held in fixed position radially and axially by said heads, gaskets between said heads and said glass, and a winding of coiled resistance wire on the surface of said insulator, said members having terminals for said resistance wire disposed within the housing formed by the heads and the glass sleeve one of the heads being separable from the associated terminal to permit the wire to be fastened to the terminals before the head is fastened to its metallic member.

12. A protective resistor comprising the combination of a substantially cylindrical insulator having a helical groove on its outer periphery, rigid metallic end pieces fixed upon' the ends of the insulator and having wire connectors, a coiled resistance wire wound into said groove and having its ends anchored to said connectors, one of said end pieces having a rigid integral extension forming a head and lying axially'beyond its connector and being provided with an axially extending flange, a glass sleeve loosely surrounding said insulator engaging said extension to have one end closed thereby, said end being cen' tered by said fiange, and a relatively thin flanged sheet metal head closing and centering the other end of the glass sleeve, said head being clamped near its central portion to the corresponding end piece to hold the glass sleeve resiliently in place, said sleeve and its end closures providing a closed insulating housing for the resistance wire.

13. A high tension protective resistance device adapted to be continuously connected in series with a high tension fuse so as to limit the current flow in case of fault condition, comprising a body of refractory insulation of relatively large diameterhaving a helical groove upon its outer surface, cast metallic end pieces fixedly secured independently of each other to the ends of the body in good thermal conductivity therewith, said end pieces having outer end surfaces substantially normal to-the longitudinal axis of the body for connection with circuit conductorsone of said and pieces having an integral circular flange forming a head, said head having an axial flange, a separate metal head at the other end of the insulating body, said head being clamped against the end surface of the other end piece and hav: ing also an axially extending flange, a glass sleeve centered by saidaxially extending flanges and 14. A high tension protective resistance device for a high tension circuit, said device being adapted to be connected permanently in circuit, a central body of insulation, metallic end pieces rigidly fixed upon the ends of the body, one of said end pieces serving as a support for the device,

said end pieces being adapted to be connectedto circuit conductors, a wire resistor wound upon said body of insulation and having its terminals connected to said end pieces, a glass sleeve concentric with but spaced from the body of insulation, metallic heads joined to said end pieces for closing the ends of the glass sleeve to form a relatively tight enclosure for the resistor, said heads having peripheral flanges for centering the glass sleeve, said flanges embracing loosely the external margins of the glasssleeve, whereby heating and cooling of the heads will not crack the glass sleeve, one of said heads being formed of relatively thin resilient metal providing a limited amount of play axially to permit expansion and contraction due to heating and cooling of the body, whereby to maintain a substantially tight closure without cracking the glass sleeve.

15. In a high tension protective resistor, the combination of an insulator comprising a generally cylindrical body of insulation having end faces and having openings in said end faces, me-

' tallic inserts at the ends of the insulator bonded to the side walls of said openings, and being thereby secured to the insulator independently of each other, said metallic inserts being electrically separated by insulation which structurally forms part of said body of insulation, said insulator having a helical groove extending substantially the full length of the body and occupying substantially the entire available lateral surface of the body, a helical coiled resistor disposed in said groove, said inserts extending endwise beyond the end face of the insulator and providing clamping faces which face axially, and having terminal portions provided with means disposed in convenient position to clamp the terminal portions of said helical resistor at the ends of the groove, said means lying substantially within the radial confines of the resistor, and enclosure means comprising a glass sleeve relatively closely surrounding the insulator, and

a removable head clamped against the end face of one insert, said head closing one end of the sleeve and having means for centering the sleeve with respect to the insulator.

16. In a high tension protective resistor, the combination of a coiled resistor, a body of insulation grooved to receive said coiledresistor, the insulator having an opening extending endwise into the end face thereof, a metallic insert bonded to the side walls of said opening and having a portion forming a fiatend face and having a portion providing a terminal to which the end of said coiled resistor may be attached, said terminal being confined substantially within the radial confines of the insulator, a glass sleeve disposed concentrically about the insulator, and a metallic head member for engaging the end of the glass sleeve and centering the same, said head member being clamped to the said metallic insert.

17. In a high tension protective resistor unit, the combination of a generally cylindrical body of insulation grooved to receive a resistance wire, a resistance wire wound in said groove, a metallic end part at each end of the insulator, said parts being fastened rigidly to the insulator independently of each other and separated electrically by insulation which structurally'forms part of said body'of insulation, a cylindrical glass enclosure for the unit, clamping means adapted to be secured to one metallic end part for engaging the glass enclosure and holding it in place, said one 6 metallic end part'p'roviding a terminal anchorage for the resistance wire, and means for securing the clamping means to said one metallic end part independently of the terminal anchorage.

5 18. In combination, a substantially cylindrical body of refractory insulation, metallic end members mounted upon said body of insulation, said body of refractory insulation having recesses in the ends thereof and said end members having 10 studs projecting into said recesses and being bonded to said body, a coiled resistance wire wound on said body under initial tension and connnecting said end members, said resistance wire tending to unwind, the turns of the coiled resistance 15 wire being spaced on said body, a sleeve of vitreaoeaies members are bonded to the body of insulation,

and after the connection of the resistance wire to said end. members has been made.

19. Ina high tension protective resistor unit, the combination of a generally cylindrical body of insulation grooved to receive a resistance wire,

a resistance wire wound in said groove, a metallic end part at each end of the insulator providing terminals for the resistance wire, said parts being fastened rigidly to the insulator independently of each other and separated electrically by insulation which structurally forms a part of said body of insulation, and a closure for the resistor k comprising a sleeve of'insulating material fairly closely surrounding the body of insulation, and

, means at each end of the sleeve cooperating with the end parts to complete the closure, one of said means being movable towards the other axially of the insulator to assemble the closure.

N CHOLAS J. CONRAD. 

